Zeolites, such as mordenite and ferrierite are known to be suitable for use as catalysts for the carbonylation of feedstocks such as methanol, dimethyl ether and dimethyl carbonate to produce the carbonylation products methyl acetate and/or acetic acid.
EP-A-0 596 632 describes a vapour phase process for the carbonylation of methanol to produce acetic acid in the presence of a modified mordenite catalyst at high temperatures and pressures.
WO 2005/105720 describes a process for production of a carboxylic acid and/or an ester or anhydride thereof by carbonylating an aliphatic alcohol or reactive derivative thereof with carbon monoxide in the substantial absence of halogens in the presence of a modified mordenite catalyst at a temperature in the range 250-600° C. and a pressure in the range 10 to 200 bar.
WO 2006/121778 describes a process for the production of a lower alkyl ester of a lower aliphatic carboxylic acid by carbonylating under substantially anhydrous conditions a lower alkyl ether with carbon monoxide in the presence of a mordenite or ferrierite catalyst.
‘Heterogeneous catalysts for the direct, halide-free carbonylation of methanol’ by Ellis et al, Studies in Surface Science and Catalysis, Vol. 111, pages 771-779, 1996, describes the catalyst preparation, performance and physical characterisation of Cu-mordenite compared to H-mordenite.
However, although the zeolites are highly effective carbonylation catalysts, it has been found that they undergo deactivation with time. Without wishing to be bound by theory, it is believed that loss in activity and/or selectivity is at least partly due to the formation of hydrocarbonaceous deposits (coke) which prevent access to the catalytically active sites of the zeolite. Thus, there remains a need for a method for treating a deactivated zeolite in order to at least partially restore activity whilst maintaining selectivity to acetyls product.